Cryopreservation of cell suspensions is to be studied. Cooling-rate, warming-rate, chemical environment, and density of cells in suspension are considered primary variables. Emphasis is on development of principles for selection of these four interacting variables for future application to successful organ preservation. Rates of cooling and warming will be automatically controlled from 0.25 to 2000 degrees/ min. Alteration in chemical environment will include varying buffer systems, using different colligative and polymeric materials, and changing ionic strength. Since cells apparently need to be frozen in the presence of protein for maximal survival, but protein molecules are too large to penetrate cells in organs, cryoprotection by stabilization of proteins already in the membrane will be attempted by the addition of suitable stabilizing ions. Phase change during freezing and thawing will be observed with differential thermal analysis and impedance measurements. Interrelations between phase change, cooling-rate, warming-rate, chemical additives present, concentration of cells in suspension, and resultant cellular damage will be studied. Extent of damage will be assayed by analysis for release of intracellular enzymes into solution and by morphological changes.